The present invention relates to the utilization of age-hardenible copper alloy for the manufacture of sideblocks or dam blocks in twin belt casting machines wherein the molten material solidifies within a gap formed in between two parallel guided belts, strips, ribbons or the like and the blocks prevent lateral outflow. Casting machines of the type to which the invention pertains and more particularly dam blocks or barriers are shown e.g. in U.S. Pat. No. 3,865,176 disclosing a twin belt or strip casting device and including metal blocks which are placed on an endless belt made of steel. These blocks are moved synchronously with the casting belts in longitudinal direction. As stated, the metal dam blocks bound the casting cavity established by the two casting strips.
The throughput of a twin belt or twin strip casting machine clearly depends decisively on the flawless functioning of many parts, including particularly the dam blocks and the chain formed by the plural blocks in this fashion. Specifically it is required that these blocks have a very high thermal conductivity in order to remove the melting and solidification heat as rapidly as possibly. In order to avoid premature wear of the side edges of the dam blocks through mechanical wear it is necessary to use a material which not only is very hard and has high tensile strength, but is also provided with a very low grain structure. It has to be observed that gaps between these blocks must be avoided since the molten material could then penetrate into such gaps. Another important aspect is fatigue; it must be made sure that following departure of the blocks from the line of casting a thermal tension shock is introduced in the blocks when cooling down or return. This shock must not cause them to crack e.g. in the edges and here particularly in the T-grooves in which they guide the steel strip. If such a thermal shock does produce cracks then very soon the particular block will simply drop out of the chain and the molten metal can escape in an uncontrolled fashion and cause havoc in the equipment at large. On the other hand it is clear that as soon as some kind of damage is detected the entire machine has to be stopped, and the casting has to be interrupted and the necessary repairs be carried out.
For testing the propensity towards the formation of cracks a method has been practiced with advantage according to which the blocks are treated for two hours at 500 degrees C and quenched in water of 25 degrees C. This is repeated and these plural thermal shocks must not produce any cracks whatsoever particularly in the zones of the T-grooves.
The material for such dam blocks thus is suggested in the U.S. Pat. No. 3,955,615 is an age hardenible copper alloy which includes form 1.5 to 2.5% nickel, from 0.4 to 0.9% silicon, from 0.1 to 0.5% chromium and from 0.1 to 0.3% iron, all percentages by weight; the remainder of course being copper. Such an alloy is used generally for equipment of the kind referred to above. However, it was found that copper alloys of this type when used specifically for making these dam blocks cause, after a relatively short operating time, the casting device to exhibit fatigue cracks particularly in the critical area of the T-grooves. Aside from a rather unsatisfactory behaviour during thermal shock testing this particular alloy has about 45% IACS which is a relatively low electrical conductivity, and, therefore, it has a relatively low thermal conductivity.
It has been proposed to make dam blocks of copper alloy that includes beryllium. Aside from certain technical advantages such an alloy might have it was found that working with this kind of material is outright dangerous to the health of the people who e.g. will finish in some form or another the blocks and come in intimate contact with that beryllium containing material.